ASCEND capabilities

The following is a summary of current ASCEND capabilities. It is intended to be a complete list. If you want a more general/introductory overview, see the ASCEND overview. The main page for accessing greater detail on these topics is our documentation index. This page emphasises the newer PyGTK-based GUI for ASCEND. An overview of the features of the older Tcl/Tk GUI is can be obtained from the TclTk screenshots.

Language features

• Equation-based language, see Equation-based Process Modeling for an overview.
• Full support for units of measurement; user never needs to worry about conversion factors.
• Hierarchical MODELs allowing modular system models built from reused components
• Procedural initialisation of models and solver parameters using METHODs
• WHEN syntax for conditional modelling also known as 'variable-structure modelling'.
• DATASET allows loading of CSV/TSV tabular data. Also Data reader which is used for interpolation/time-series datasets (for DAE problems, say).
• Differential as well as algebraic equations can be expressed
• Constants are declared separately from variables
• Multi-modal models with SWITCH statement (switching based on values assigned to constants).
• Externally-defined equations ('external relations') can be added to models via shared libries and the IMPORT statement
• Can run arbitrary Python code in METHODs via ExtPy linkage, useful for custom plotting, reporting, and model initialisation.

Solver features

• Detection of singular and non-square equation systems; user is advised on what modifications would help to make system square.
• Steady-state QRSlv non-linear algebraic (NLA) solver with block decomposition.
• Non-linear programming (NLP)/optimisation solvers IPOPT (open source) and CONOPT (commercial).
• Mixed-integer programming solver HiGHS.
• ODE and DAE solvers for dynamic modelling: IDA, RADAU5, LSODE
• Some preliminary support for dynamic switching models with boundaries, see integration of conditional models.
• Solver parameters can be set from within the model code (see SOLVER and OPTION statements). Model language allows solving of whole models or just a sub-model.
• New solvers can easily be added, implemented as external libraries that access our Solver API.

GUI features

• View all aspects of a model in a hierarchical tree view
• FIX and FREE variables interactively, set their values, and quickly re-solve the model.
• Interactive exploration of the numerical/convergence behaviour of the model
• Capture the state of selected variables for export/plotting via Observer functionality
• View incidence matrix showing block-decomposed structure of steady-state systems
• Diagnose blocks in the model which have been giving numerical problems
• Observer/study feature: sweep variables and solve each time, to generate tabular/plot outputs from a flowsheet.
• View incidence graph (aka dependency graph) for solution process
• Plot the time-varying values from the solution of dynamic problems
• Alpha-quality canvas-based modeller for ASCEND allows 'wiring up' of graphical 'blocks' to construct complex flowsheets

Thermodynamics and Engineering features

• models/thermodynamics.a4l code for basic-level accuracy of pure species as well as mixtures
• FPROPS code for accurate calculation of pure species properties
• linkage to freesteam library for calculation of steam properties by official IAPWS-IF97 correlations.
• A range of models for [[Energy system modelling with ASCEND|energy system modelling], including Brayton cycle, Rankine cycle and several solar thermal energy component models.
• Models of mixers, separators and reactors for chemical process modelling (eg models/flash.a4l)
• A growing model library with a wide range of examples and reusable models.